By 'multi-level' are you referring to a mix of freeway and tollway lanes, or physically multi-level, i.e. double-decked? The only toll roads in the LA area are in Orange County(San Joaquin Hills-73, Foothills-241, Eastern-261 & 133, and Riverside Freeway-91), but only the Riverside Freeway has both freeway lanes and managed toll lanes down the median. None are known for being multi-level, if that means double-deck. There is talk of double-decking the Riverside Freeway, but it is so expensive that there is serious consideration of building a multi-mile tunnel through the Santa Anna Mountains several miles to the south(though there are also geographical/travel pattern advantages to the tunnel route). Most of these tollways were designed with a median reserve for HOV/HOT/managed(congestion priced tolling) lanes or future transit use. IIRC, the Riversides managed lanes don't just vary price with the congestion, but also are restricted to high occupancy vehicles during rush hour. A good idea, and it is coming to Texas(Katy Freeway rebuild is one example), but it is not the only solution needed.
Denton-Dallas light rail ("commuter rail") has been tried, ran a very few years, at a huge cost per round-trip - about $42 in 2003 dollars. And it failed, massively in debt.
First off, light-rail and commuter rail are very different modes of transit. The former usually requires electrification, can run on streets but not existing freight railroads(because of FRA safety regulations), operates frequently(every 5-20 minutes all day) and runs about 20-60+ million per mile to construct. That is NOT what DCTA is proposing. Commuter rail can use existing freight railroad tracks, but not streets, operates less frequently(every 15-30 minutes in rush and less frequently or no service outside of rush hour) and thus is often much cheaper to build, generally $3-15 million per mile.
Please give me an approximate year when the commuter trains you claim ran between Denton and Dallas quit running. The service I know of, the electrified Denton Interurban, quit running in 1932! Hardly comparable, as things have changed since then. That's like saying the North Dallas Tollway shouldn't be extended north, because there were not suburbs in Frisco in the 1930's.
Just 30 years ago the much more expenisve Dallas-Plano lightrail line would have been a failure, but now it is a success as growth congestion, employment, development, and commuting patterns have changed greatly. Despite everyone who said it would not work.